Video signal processing circuit

Abstract

PURPOSE: To prevent deterioration in picture quality by detecting a peak voltage among 3 colors of color difference signals and decreasing the color saturation and contrast when voltage difference level between the amplitude voltage and a negative luminance signal reaches an input voltage in matching with the saturation of a drive transistor (TR). CONSTITUTION: In the case of receiving a color bar, each color difference signal is led through diodes 20, 21, 22 and a peak value among the signals is outputted. The voltage setting value of a Zener diode 23 is decided so that a TR 25 is turned on at a voltage difference of 4.05V between the peak voltage and the voltage of the luminance signal based on the saturation condition. For example, suppose that a potential difference of 4.05V or over takes place parts A, B in waveform diagrams d, e, then the TR 25 is turned on at the parts and the collector voltage is decreased, then the diodes 29, 31 are conductive and the color saturation control voltage and the contrast control voltage area also decreased as shown in figures g, h. Thus, the saturation of the cathode drive TR is prevented. COPYRIGHT: (C)1990,JPO&Japio

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Cited By (3)

    Publication numberPublication dateAssigneeTitle
    EP-0812107-A1December 10, 1997THOMSON multimediaVorrichtung zur Einstellung des Kontrasts von Videobildern
    FR-2749731-A1December 12, 1997Thomson Multimedia SaDispositif de regulation de contraste d'image video
    US-5940144-AAugust 17, 1999Thomson Multimedia S.A.Device for regulating the contrast of video images